The present invention relates to a photopolymerizable composition comprising (a) a polymeric binder, (b) a polymerizable compound containing at least two terminal ethylenically unsaturated groups and having a boiling point above 100.degree. C., and (c) a 1,3,10-triazaanthracen-4-one as the photoinitiator.
Photopolymerizable compositions which contain the components (a) and (b) and a polynuclear heterocyclic compound as the photoinitiator are known. In German Patent No. 2,027,467 (equivalent to British Patent Specification No. 1,354,541), specific derivatives of acridine and phenazine are described as initiators. German Patent No. 2,039,861 (equivalent to U.S. Pat. No. 3,765,898) discloses similar compositions containing quinoxaline derivatives or quinazoline derivatives as initiators.
All these compounds act as excellent initiators when they are irradiated with actinic light, particularly from light sources emitting in the near ultraviolet region. However, they are not optimally adapted to light sources which have an increased emission in the visible spectral region, such as metalhalide doped gas discharge lamps.
In order to compensate for this deficiency, published European Patent Application No. 102,586 describes photoinitiators comprising 1,3-diaza-9-thiaanthracene-2,4-diones, the absorption range and initiating activity of which extend further into the visible spectral region. These compounds are comparatively easily prepared, but they require a reaction step using an aromatic thiol, in which obnoxious odors are emitted so that special protective measures are necessary. Due to the structure of their parent substance, the compounds also tend to have a limited solubility in many solvents and, consequently, their applicability is restricted.